By Jason Lewis, Local Democracy Reporter

Campaigners have accused Southern Water of failing to publish River Itchen pollution findings promptly with testing showing extremely high levels of E. coli.
• Council declares no confidence in Southern Water over River Itchen pollution

 

Gavin Millar, of Friends of the Itchen Estuary, has written an open letter to Southern Water chief executive Lawrence Gosden calling for accountability, transparency and urgent public-health action.

It has emerged water testing carried out during autumn 2025 showed that E. coli and enterococci levels were consistently high.

Guardians of the River Itchen carrying out water sampling. Photo: Gavin Millar

However, the results were not published on Southern Water’s website until recently.

Mr Millar’s letter asks Southern Water to apologise for what he describes as withholding the data, amend its ‘Rivers and Seas’ website and provide Southampton City Council with funding for sewage-pollution warning signs.

The letter said: “These results were not published, despite their clear public health significance.”

Southern Water’s Itchen Estuary 2025 faecal pathogen investigation tested water from seven upper estuary locations and one river location on ten separate days.

Mr Millar said only one of these days recorded combined sewer overflow activity but the investigation returned average E. coli levels at 5,700 colony-forming unit (cfu) per 100 millilitres and a peak level of 70,000 cfu per 100 millilitres.

For an estuary to have a ‘satisfactory’ water quality rating from the Environment Agency, water testing must show a 90 per cent probability that any given sample will be below 500 cfu per 100 millilitres.

Mr Millar, pictured left, said Southern Water has been aware of the ‘very high’ faecal-pathogen load from Portswood Wastewater Treatment Works for at least a decade, citing the 2016 water quality impact assessment the company commissioned.

He said this assessment reported annual E. coli load from continuous effluent was very high and included an estimate that it was 34 times higher than the annual E. coli load from storm overflow discharges.

Mr Millar told the Local Democracy Reporting Service he was aware of people who had got seriously ill after swimming or carrying out water-based activities on the River Itchen.

He said: “No system is in place for reporting these illnesses.

“I think there is very good reason to believe this is just the tip of the iceberg.

“This issue falls into a chasm between the Environment Agency’s focus on ecology and public health who are only interested if there is a significant number of reported cases, but there is no mechanism to report them.”

Mr Millar said while wastewater treatment works at Chickenhall in Eastleigh and Millbrook in Southampton have pathogen-killing effluent sanitation, no such provision is in place at Portswood.

Friends of Itchen Estuary have been carrying out their own water testing as part of their advocacy and campaigning efforts.

A Southern Water spokesperson told the Local Democracy Reporting Service the 2025 investigation report was scheduled to be published this month as agreed with the Lower Itchen Steering Group.

It was presented to the steering group in June and is live on the firm’s website.

On the ‘Rivers and Seas’ website, the company said it provides real-time information on storm overflow activations rather than guidance for people wanting to use the river.

The spokesperson said the utility provider had committed to installing public signage in the vicinity of Portswood Wastewater Treatment Works alerting people to discharge points including storm overflows, final effluent and surface water outfalls.

These signs will not offer warnings or advice on bathing.

Dr Nick Mills, Southern Water’s director of environment and innovation, said: “We understand the importance of the River Itchen to our community, which is currently rated ‘good’ in ecological status.

“Our sites are operating within permits set by the Environment Agency and we continue to work closely with the regulator and stakeholders including the Lower Itchen Steering Group to better understand and address the various factors impacting water quality.

“We’re investing more than £160 million to improve river health, including £70 million specifically for the Itchen, by upgrading wastewater treatment works and boosting river monitoring.”

Previously
Catch-22 over safe river bathing C
Council declares no confidence in Southern Water over River Itchen pollution
Councillor warns of ‘very severe risk’ of illness for river swimmers

 Photo of Gavin Millar courtesy Gavin Millar